The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information to users around the world. It was developed by the US Department of Defense in the 1970s and became fully operational in 1995. GPS uses 24 satellites and ground control stations to transmit timing signals that allow GPS receivers to calculate their precise location. It has both military and civilian applications in areas like navigation, mapping, timing, and tracking.

1. Global Positioning System

2. What is the GPS?
 The Global Positioning System (GPS) is
a space-based satellite navigation system
that provides location and time information
in all weather, anywhere on or near the
Earth, where there is an
unobstructed line of sight to
four or more GPS satellites
 Developed by
Department of Defense

3. History of the GPS
 1973—The GPS project was developed to
overcome the limitations of previous
navigation systems
 1994—GPS Was Created and realized by
U.S. Department of Defense (DoD)
and was originally run with 24
satellites

4. History of the GPS
 1993—Indicating a
full constellation (24
satellites) was
available
 1995—full operational
capability
 May 2000—Military
accuracy available to
all users

5. Components of the System
Space segment
 24 satellite vehicles
 Six orbital planes
 Inclined 55o with respect to
equator
 Orbits separated by 60o
 20,200 km elevation above
Earth
 Orbital period of 11 hr 55
min
 Five to eight satellites
visible from any point on
Earth

6. The GPS Constellation

7. GPS Satellite Vehicle
 Four atomic clocks
 Three nickel-cadmium
batteries
 Two solar panels
 Battery charging
 Power generation
 1136 watts
 S band antenna—satellite
control
 12 element L band antenna—
user communication
Block IIF satellite vehicle
(fourth generation)

8. GPS Satellite Vehicle
 Weight
 2370 pounds
 Height
 16.25 feet
 Width
 38.025 feet including
wing span
 Design life—10 years

9. Components of the System
User segment
 GPS antennas & receiver/processors
 Position
 Velocity
 Precise timing
 Used by
 Aircraft
 Ground vehicles
 Ships
 Individuals

10. Components of the System
Ground control segment
 Master control station
 Schreiver AFB, Colorado
 Five monitor stations
 Three ground antennas
 Backup control system

11. GPS Communication and Control

12. GPS Ground Control Stations

13. How does GPS work?
 Satellite ranging
 Satellite locations
 Satellite to user distance
 Need four satellites to determine position
 Distance measurement
 Radio signal traveling at speed of light
 Measure time from satellite to user
 Low-tech simulation

14. How does GPS work?
Pseudo-Random Code
 Complex signal
 Unique to each
satellite
 All satellites use
same frequency
 “Amplified” by
information theory
 Economical

15. How does GPS work?
 Distance to a satellite is determined by measuring how
long a radio signal takes to reach us from that satellite.
 To make the measurement we assume that both the
satellite and our receiver are generating the same
pseudo-random codes at exactly the same time.
 By comparing how late the satellite's pseudo-random
code appears compared to our receiver's code, we
determine how long it took to reach us.
 Multiply that travel time by the speed of light and you've
got distance.
 High-tech simulation

16. How does GPS work?
 Accurate timing is the key to measuring
distance to satellites.
 Satellites are accurate because they have
four atomic clocks ($100,000 each) on
board.
 Receiver clocks don't have to be too
accurate because an extra satellite range
measurement can remove errors.

17. How does GPS work?
 To use the satellites as references for range
measurements we need to know exactly where they are.
 GPS satellites are so high up their orbits are very
predictable.
 All GPS receivers have an almanac programmed into
their computers that tells them where in the sky each
satellite is, moment by moment.
 Minor variations in their orbits are measured by the
Department of Defense.
 The error information is sent to the satellites, to be
transmitted along with the timing signals.

18. GPS Position Determination

19. System Performance
 Standard Positioning
System
 100 meters horizontal accuracy
 156 meters vertical accuracy
 Designed for civilian use
 No user fee or restrictions
 Precise Positioning
System
 22 meters horizontal accuracy
 27.7 meters vertical accuracy
 Designed for military use

20. System Performance
Selective availability
 Intentional degradation of signal
 Controls availability of system’s full capabilities
 Set to zero May 2000
 Reasons
 Car navigation
 Adoption of GPS time standard
 Recreation

21. System Performance
 The earth's ionosphere and atmosphere
cause delays in the GPS signal that
translate into position errors.
 Some errors can be factored out using
mathematics and modeling.
 The configuration of the satellites in the
sky can magnify other errors.
 Differential GPS can reduce errors.

22. Application of GPS Technology
 Location - determining a basic position
 Navigation - getting from one location to
another
 Tracking - monitoring the movement of
people and things
 Mapping - creating maps of the world
 Timing - bringing precise timing to the
world

23. Application of GPS Technology
 Private and recreation
 Traveling by car
 Hiking, climbing, biking
 Vehicle control
 Mapping, survey, geology
 English Channel Tunnel
 Agriculture
 Aviation
 General and commercial
 Spacecraft
 Maritime

24. GPS Navigation

25. Military Uses for the GPS
Operation Desert Storm
 Featureless terrain
 Initial purchase of 1000 portable commercial
receivers
 More than 9000 receivers in use by end of the
conflict
 Foot soldiers
 Vehicles
 Aircraft
 Marine vessels

26. Handheld GPS Receivers
 Lowrance iWay350c
This is great value for
a full-featured turn-by
turn GPS navigation
system.
 Cobra NavOne 450
This system's 5-inch
screen and integrated
live traffic data set it
apart from other GPS
devices.

27. GPS Operation
 “Waypoint” or “Landmark”
 “Track” or “Heading”
 “Bearing”
 CDI
 Route
 Mark
 GOTO
Mobile phone GPS tracking